Firstly, thanks to the helpers already in place, regular clothes don't have to fit tightly anymore. Take some of my clothes for example, they don't have to stick to the body.
Secondly, well you can always tweak the end result or add details afterwards.
Try it out with a simple cape and post the results here, with a picture or whatever. If it doesn't work well, let us know what didn't work and maybe before you know it it's fixed. The thing with special clothes is not that they are not supported, just that nobody experimented with them yet. By doing some experiments you could be of a lot of help to the MH project. There's a lack of artists

Then, regarding the second: I have recently experimented some more with creating masks, and I used the "project UVs" button in the clothes script. This works pretty well, the only problem is in the areas where the seams are on the human mesh. You get a lot of faces spanning the whole width of the body or suddenly jumping from the body island to the hands or something. You don't want that. So you want to move those faces to just one place, so they're not too big. The problem is that there was no seam between them so the vertices of those faces and their neighbours are shared. Meaning that if you move some vertices, you have the same problem with another face that stretches too far.
To solve this problem: select only one edgeloop at a time in the 3D view. Select an edgeloop that is near the seams of the human mesh and in UV editor move the vertices to the right place. This way you uncouple the shared vertices.
Place a good texture on the uv map, for example the body specular map. In 3D view all faces that have stretched UVs will look weird when theyre textured. This helps you select the right edgeloops.
This is the workflow I have come up with now, I have yet to see whether this is a good one.